1. Field of the Invention
The present invention relates to a stroboscopic instrument, and in particular to a stroboscopic instrument having a gate-controlled switching element.
2. Related Art Statement
Known as an element for controlling flashing of light in recent camera stroboscopes is a gate-controlled switching element such as IGBT (Insulated Gate Bipolar Transistor). For example, Japanese Patent Application Laid-open No. Sho-64-17033 discloses a stroboscope that employs an IGBT wherein the IGBT is turned on in response to a flash command trigger signal and turned off in response to a flash end command.
The prior art disclosed in Patent Application No. Sho-64-17033 requires a power supply for controlling the gate of the switching element, thereby resulting in added cost and needing extra space.
To resolve such problems, Japanese Utility Model Application No. Hei-4-96721 has proposed an electronic flashing device wherein its main capacitor feeds beforehand voltage to the control terminal of a switching element only while the power switch is on.
Japanese Patent Application Laid-open No. Hei 6-302389 has disclosed a newly developed low-voltage gate-drive type switching element which is assuredly triggered by a gate voltage ranging from 4 volts to 8 volts. Such a switching element can be directly driven by a relatively low voltage power supply that is shared with a control circuit.
In the techniques proposed by the above cited Patent Application 64-17033 and Utility Model Application 4-96721, however, a high voltage from a stroboscope charging circuit is directly applied to a gate-controlled switching element to control it. Since the voltage of the high voltage stroboscope charging circuit is used, its circuit configuration is complicated, leading to a bulky design. Furthermore, since the switching element itself has to withstand a high voltage, the device is inevitably costly and bulky in size.
In the technique disclosed in the above cited Patent Application 6-302389, the above-mentioned high-voltage switching element is dispensed with, and a relatively low voltage power supply is used to control the switching element. This technique is particularly useful in a stroboscope which is operated on a battery power supply of about 6 volts (for example, two 3-volt batteries in series). Today, however, cameras that are operated on a lower voltage power supply as low as 3 volts, for example, are increasing in use. The above technique is difficult to implement in such low-voltage driven cameras.
When the gate-controlled switching element of which gate control voltage is 4 to 8 volts is mounted on the stroboscope with a low-voltage power supply as low as about 3 volts, the switching element is accompanied by the following inconveniences.
Namely, a low-voltage power supply as low as 3 volts cannot directly drive the low-voltage driving switching element (its gate control voltage from 4 volts to 8 volts). When the output of the stroboscope charging circuit in the stroboscope is also used as a control voltage for the switching element, the following problems will arise.
1) An increased power consumption shortens the life of the low-voltage power supply.
2) The output voltage of the low-voltage power supply is substantially reduced when a sufficient current margin is not assured during stroboscope charging.